Under the teachings of the prior art, resistance training primarily relies on a user's raising, lowering, or otherwise manipulating what are commonly referred to as free weights, which often take the form of weighted plates that are selectively applied to or removed from barbells or dumbbells to permit an adjustment of the overall weight to be manipulated. Other free weights are fixed in configuration, such as by having a central handle portion with first and second bulbous weights at opposed ends thereof.
While such free weights can be raised, lowered, and otherwise manipulated with good effectiveness, their use is limited. For example, although the individual components may be somewhat portable, the overall free weight system necessary to provide selective resistance weights is difficult to transport due not only to the inherent weight of the components but also due to the multiplicity of awkward plates, bars, and fasteners that would need to be packed and carried. Free weights are further limited in that their operation relies on the effects of gravity in relation to the various levers and propulsion systems that can be formed by the human body. It will also be appreciated that free weights are of substantially no use in weightless environments. Even under the force of gravity, resistance provided by free weights will vary, sometimes undesirably, with the moment arm over which the user's arms, legs, or other body parts act.
A number of inventors have sought to provide portable exercise systems and exercise apparatuses not dependent on free weight. For example, in U.S. Pat. No. 4,208,049 for a Constant Force Spring Powered Exercising Apparatus, Wilson teaches what is characterized as a multi-functional exercise apparatus that employs a plurality of constant force springs. The springs can be chosen individually or in groups to provide a selected resistance during exercise. However, the Wilson system is complex in construction and requires mounting to a large support platform that again renders the system effectively non-portable. With U.S. Pat. No. 5,618,249 for Unidirectionally Adjustably Resistant Recoilers and Portable Exercise Devices, Marshall discloses an upper body exercise device with two spring-loaded recoilers retained by a waist pouch. The system is advantageous for its portability, but the user is limited to the resistance of a single recoil mechanism for each arm, leg, or other body part. With that, the system is inherently limited in its range of resistance and use. Still further, in U.S. Pat. No. 5,733,231 for an Exercise Device with Variable Resistance, Corn et al. discloses an exercise device with resistance mechanisms to resist each of a plurality of cords as the cords are withdrawn from a retracting mechanism. While the system provides removable disks for incrementally increasing resistance force, the retention, removal, and selection of the several resistance disks are relatively complex and do not appear to be as intuitive as would be desired for the average user. Also contributing to the state of the art is United States Patent Application Publication No. 2002/0025891 of Colosky, Jr. et al. for a Gravity-Independent Constant Force Resistive Exercise Unit. There, Colosky describes an exercise unit with modular resistive packs retaining constant torque springs to provide constant forces opposing the withdrawal of an exercise cable. While a user can select from multiple resistive packs, the overall system is disposed in a large housing and could not be readily portable or retained easily in relation to a human body. Accordingly, the application of the exercise unit is inherently limited.
Still other exercise systems of the prior art rely on simple coil springs or elastic cords that are attempted to be retained by the user's own body to provide resistance. While such systems are advantageous for their simplicity and while they may permit a user to alter resistance forces by physically adding or removing springs or bungees, they are cumbersome to use and can present dangers to the user due to misuse and malfunction.
Accordingly, it will be appreciated that there is a need for an exercise system capable of selective resistance adjustment by the user that enables consistent, user-selected resistance over an exercise movement. There is also a demonstrated need for an exercise system that is readily portable, such as by being able to be retained and transported by a direct coupling to the human body. Still further, there is a recognized need for an exercise system that is safe and comfortable in use while permitting an adjustment of resistance in a convenient and intuitive way.